My first idea was to create an <article> for each class, with a first section Detailed Description, then another one Member Function Documentation (mapping the structure of the original documentation); avoiding those sections would even be better, as they add no semantics to the document. This second section would have contained a <classsynopsis> with all the methods in <methodsynopsis> and their documentation (i.e. a set of paragraphs for each method). However, a <methodsynopsis> does not allow textual content as <para>.
<?xml version="1.0" encoding="UTF-8"?>
<db:para>The <db:link xlink:href="qlowenergycharacteristic.html"
>QLowEnergyCharacteristic</db:link> class stores information about a Bluetooth Low
Energy service characteristic.</db:para>
<!-- ... -->
<db:title>Member Function Documentation</db:title>
<db:para>Construct a new QLowEnergyCharacteristic. A default-constructed instance of this class is always invalid.</db:para>
<db:para>Construct a new QLowEnergyCharacteristic that is a copy of other.</db:para>
<!-- ... -->
. It uses one section per class, starting with a <classsynopsis>, then nested sections afterwards for the methods if there is anything to say about them.
This way of doing things makes me feel dubious, as there is no direct link between the class and its method: each method basically copies a part of the class definition. In my case, as all methods have a few words about them, there is a high risk of someone changing (inadvertently) a letter or anything (<classsynopsis> could even be avoided); and at the semantic level, the notion of class or method documentation would be completely lost (as the real documentation would just be a set of sections).